Sunday, January 15, 2012

In this book, Stephen Mumford and Rani Lill Anjum present their theory of causal dispositionalism, that is, causation based on dispositional properties, or powers. I highly recommend it to anyone interested in the philosophy of causation.

Powers do the causal work in our world, according to the authors: effects are brought about by powers manifesting themselves, and the manifestation is itself a further power or set of powers.

A central idea is that powers don't necessitate their manifestations - they dispose toward them. Causality has long been associated with the idea of necessity, and necessity (and the sense of constant conjunction) is too strong to describe causation. The main insight here is that other factors can prevent or interfere with the expected manifestation (and, indeed, they often do).

To help demonstrate how a disposition can be enhanced or, importantly, hindered by other powers, the authors develop a vector addition diagram. Only when the sum of vectors (with various strengths and directions) exceeds some threshold do we get the manifestation. They extend the model to more complex scenarios to argue that the model is robust enough to explain non-linear and even "emergent" behavior.

In addition to arguing strongly against necessity, the authors want to overthrow another usual notion. The authors reject as misguided the typical "two-event" conception of causation, where cause is temporally prior to effect, in part because no one has a compelling account of how you get from one to the other. Instead causes and effects are simultaneous - they are two aspects of a temporally extended process which brings about a change.

An important and creative part of the book explores the distinctive modality of dispositions in more depth. Dispositional modality (weaker than necessity but stronger than "pure" contingency) is the primitive and fundamental modality of nature. We derive necessity and possibility from our prior experience with dispositionality. Mumford and Anjum argue that we do indeed perceive causation, and present what they see as the clearest examples of this in the case of bodily sensation and specifically proprioception.

The book concludes with a compelling application: showing how the theory fits with processes studied in biology and genetics.

As touched on at the end of my prior post, one possible
challenge to models of causation, including the thesis of causal
dispositionalism presented in this book, is the fact that causation doesn’t
seem to comport well with physics. The
authors acknowledge this in their first chapter, referencing Russell’s
discussion in his "On the Notion of Cause” (1913). The issue is that dynamical equations
associate states of a system with points in time, but nowhere do they invoke
the idea of causal production. They are
symmetric with regard to time, where causation is not. Mumford and Anjum respond in a couple of
ways. First, they say, the fact that
causation doesn’t appear at the level of physics doesn’t mean it isn’t present
at larger scales: the reducibility of
all phenomena to physics is a controversial idea which we are not compelled to
accept. We don’t know that physics
represents a special fundamental level of reality in any case. And given the provisional nature of scientific
theories, should we let them trump our metaphysical reasoning?

This issue recurs as the book progresses. In Chapter 4, the authors show how the
composition of powers in causal situations can plausibly model emergent
phenomena in the form of novel powers.
So the theory is robust if it does turn out that reduction of the
phenomena in the special sciences isn’t possible. And the final chapter of the book (ch.10) presents
an interesting and persuasive application of the theory by showing how causal
dispositionalism fits quite well with examples of processes studied in biology
(including genetics).

Just like the situation in philosophy of mind, one must be
cautious about drawing metaphysical conclusions from the perceived character of
formal physical theory.